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1、Profile Guidelineshttp:/ Heating RampInitial Heating RampObject is to get profile to pre-heat stageLimited by board & components (thermal shock)Explosive out-gassing from the solder paste will only occur under extreme conditions (eg laser soldering)Common ramp-rates are 1-3C.s-1This stays the same f
2、or lead free Pre-heat SoakPre-Heat SoakThe pre-heat allows all areas of the board to reach a similar temperature before reflowWith modern ovens it is possible to reduce or eliminate the “plateau” part of the profileThere is no specific activation temperature for solder pastes. HoweverThe activators
3、become more effective once they are molten or dissolved in molten resinPre-Heat SoakRosins begin to soften and flow at temperatures between 70- 120C A simple law of chemistry says that reactions become faster at higher temperatures During the pre-heat (in aerobic reflow), oxidation will occur on exp
4、osed metal surfacesPre-Heat SoakAlthough the pre-heat soak for lead based alloys is considered to be between 100 150 centigrade.This will increase to 120 170 for Pb free.The time remains roughly the same at 90 150 secondsIf a plateau profile is run we would recommend going from this to reflow spike
5、as quickly as is safe to achieve.Reflow SpikeReflow SpikeThis is when the soldering occursAll areas must exceed the melting point of the alloy to allow powder particles to coalesce, wet the surfaces and fill capillariesA higher temperature will lower the surface tension of the solder and increase th
6、e efficiency of the fluxReflow SpikeA higher temperature will increase oxide formation, discolour residues & board and may damge componentsA good reflow spike is usually about 30-40C above the liquidus of the alloy (eg. 210-220C for Sn62) and will be above the melting point for 30-60 secondsFor Pb f
7、ree this is also 30 60 seconds (90 in extreme soldering conditions. The temperature need only be from 232 245 depending on the medium used.Solder SolidificationSolder SolidificationRapid cooling will give bright shiny jointsSlow cooling allows more dissolution of substrates which will give rough or dull looking joints. Taken to extreme, this can lead to de-wetting and poor strengthThe boards should be as cool as possible before being handled for Health & Safety reasons as well as ensuring that no joints are disturbed whilst molten
